The structures, functions and distributions of receptors and transporters in the nervous system and neuroendocrine tissues are being studied. A cDNA encoding a glycine transporter has been isolated and shown to be one of two alternative transcripts (mRNA) for two protein isoforms derived from a single gene. Two vesicular monoamine transporters have been cloned. The distributions of these transporters and the serotonin transporter have been and are being determined using in situ hybridization histochemistry (lSSH) in adult and embryonic rat tissues. Regulation of serotonin transporter function by receptor-activated post- translational modifications (i.e., phosphorylation) has been demonstrated, and the molecular mechanism of these effects continues to be studied. Effect of altering serotonin receptor function either by using transgenic animal models or by drug treatment in vivo are being determined. The functional consequences of altering amino acid sequence of serotonin receptors by site-directed mutagenesis has been studied. Neuronal models in cell culture have been and continue to be developed for functional studies of receptors and transporters in vitro. Further functional studies based on the structure and distribution of the cloned cDNAs have been undertaken.